Here's why. They read how robots might be scanning those cover letters. They become hyper vigilant then about front-loading keywords and key phrases. Depending on the job, those might be "know SEO," "can operate WordPress," "have MBA."
Without them, the robots will eliminate the letters in the first round. After all, more than 300 can come in for any advertised job.
After they have inserted the necessary keywords, then they simply go through the motions in the rest of the letter. That is, they present a laundry list of credentials. Those don't directly tell their story. Likely, if the letter has made it beyond the robots and gets to a human being that human being will toss it. After all, the hiring agent and the applicant are not connecting. Would you hire someone you can't connect with?
By "not connecting," I mean the applicants are not helping that human being understand how they can do the job better than all the other candidates.
Yes, applicants have to make it explicit why they must hire you. You let that human being know your edge. You explain how you can get the results on this job because you have achieved amazing outcomes for other employers or clients. You provide examples. You quantify. Profits went up 34% in 18 months.
And, you tell the human being how useful for the two of you to meet. In that way you can get a deeper knowledge of the organization's opportunities and pain points.
The objective of the cover letter is to get you an interview. That's what you are gunning for in the last paragraph. Increase the odds of landing that interview by telling the human being how much you are looking forward to hearing back from him or her.